WO1991007712A1 - Simple surge control for compressors with improved response - Google Patents

Simple surge control for compressors with improved response Download PDF

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Publication number
WO1991007712A1
WO1991007712A1 PCT/US1990/006217 US9006217W WO9107712A1 WO 1991007712 A1 WO1991007712 A1 WO 1991007712A1 US 9006217 W US9006217 W US 9006217W WO 9107712 A1 WO9107712 A1 WO 9107712A1
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WO
WIPO (PCT)
Prior art keywords
pressure
line
compressor
restriction
accordance
Prior art date
Application number
PCT/US1990/006217
Other languages
French (fr)
Inventor
Malcolm Mcarthur
Original Assignee
Sundstrand Corporation
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Sundstrand Corporation filed Critical Sundstrand Corporation
Publication of WO1991007712A1 publication Critical patent/WO1991007712A1/en

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Classifications

    • G—PHYSICS
    • G05—CONTROLLING; REGULATING
    • G05D—SYSTEMS FOR CONTROLLING OR REGULATING NON-ELECTRIC VARIABLES
    • G05D16/00—Control of fluid pressure
    • G05D16/20—Control of fluid pressure characterised by the use of electric means
    • G05D16/2006—Control of fluid pressure characterised by the use of electric means with direct action of electric energy on controlling means
    • G05D16/2013—Control of fluid pressure characterised by the use of electric means with direct action of electric energy on controlling means using throttling means as controlling means
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
    • F04D—NON-POSITIVE-DISPLACEMENT PUMPS
    • F04D27/00—Control, e.g. regulation, of pumps, pumping installations or pumping systems specially adapted for elastic fluids
    • F04D27/02—Surge control
    • F04D27/0207—Surge control by bleeding, bypassing or recycling fluids

Definitions

  • a conventional ⁇ P sensor 24 which has a first gas line 26 coupled to the throat 28 of venturi 16 and one side of a diaphragm 29 which is illustrated symbolically and a second gas line 30 coupled to the upstream side 18 and to a second side of the diaphragm.
  • the ⁇ P sensor 24 functions as a differential pressure transducer to produce a control signal for controlling the opening of a servo controlled valve 32 to dump pressurized air overboard when the flow rate from the outlet 22 drops substantially which is indicative of a surge condition as will be described below.
  • the servo control valve 32 has an actuator 34 which causes the body of the valve 36 to move between opened and closed states in response to the aforementioned control signal.

Abstract

A compressor with surge control in accordance with the invention includes a rotor (12) receiving gas at an inlet and providing pressurized gas at an outlet; an outlet line (14) coupled to the outlet for providing pressurized gas; a flow measuring device (16) disposed in the outlet gas line for sensing the flow of gas in the line which causes a pressure drop in the outlet line; a bypass valve (32) disposed in the outlet line upstream of the inlet of the flow measuring device which has an open state and a closed state controlled by a control signal with the valve in the open state permitting pressurized gas discharged from the compressor to be discharged from the outlet line prior to the flow to the flow measuring device; and a pressure sensor (24) having a first line (27) coupled to the flow measuring device and a second conduit (31) coupled to the outlet line upstream of the flow measuring device with the first conduit having a pressure propagation time shorter than a pressure propagation time of the second conduit, the pressure sensor producing the control signal in response to a drop in the pressure across the pressure sensor below a threshold which causes the bypass valve to open.

Description

Description Simple Surge Control For Compressors With Improved Response
Technical Field The present invention relates to surge controls for centrifugal and axial compressors and to pressure transducers with improved response differential pressure detection of fluid pressure.
Background Art Fig. 1 illustrates a prior art compressor of the type utilized in airframes for providing pressurized air to the cabin which includes a surge protection system. The prior art system 10 includes a compressor 12 which is driven by a power takeoff from a turbine (not illustrated) to intake air at a pressure PA and output air at a increased pressure P0 to an outlet line 14. The outlet line 14 contains a venturi 16 which causes a pressure drop between the upstream side 18 of the outlet 14 and the downstream side 20 when air is flowing to the outlet 22 which is an airframe cabin. Surge protection is provided by a conventional ΔP sensor 24 which has a first gas line 26 coupled to the throat 28 of venturi 16 and one side of a diaphragm 29 which is illustrated symbolically and a second gas line 30 coupled to the upstream side 18 and to a second side of the diaphragm. The ΔP sensor 24 functions as a differential pressure transducer to produce a control signal for controlling the opening of a servo controlled valve 32 to dump pressurized air overboard when the flow rate from the outlet 22 drops substantially which is indicative of a surge condition as will be described below. The servo control valve 32 has an actuator 34 which causes the body of the valve 36 to move between opened and closed states in response to the aforementioned control signal.
Fig. 4A illustrates the operation of the surge control of Fig. 1. During normal operation, the pressure drop across the venturi 16 is equal to the difference between the pressures P0 and Pv which is the pressure in the throat 28 of the venturi. As illustrated in Fig. 4A up to time T-_ the outlet 22 is unrestricted which causes a pressure drop equal to the difference between PQ and Pv across the venturi 16. When the compressor is operating up to time T as illustrated in Fig. 4A, the signal applied to the servo controlled valve 32 maintains the valve body 36 closed so that all air being discharged from the compressor is discharged from outlet 22. At time -^ , a restriction occurs in the outlet 22 which causes the flow rate to drop and the pressure to rise substantially and rapidly in outlet line 14. As a consequence, the pressure rises rapidly in the first gas line 26 and the second gas line 30 with the relative difference in pressure in the two conduits decreasing up to point T2 in time at which the pressures are closer in value (equal if the outlet 22 is completely closed) in the first and second gas lines causing the ΔP sensor 24 to output a signal to the servo controlled valve 32 which causes the valve body 36 to open to dump air overboard to prevent a surge condition. The time delay between time at which the pressure perturbation first occurs at the venturi 16 and T2 at which time the pressure drop between the upstream side 18 and the throat 28 of the venturi drops to a value that would open the valve 36 makes it necessary that the compressor be operated on a load line at a point displaced from the "SURGE LINE", such as the "TYPICAL OPERATING POINT" on the "CONSTANT SPEED LINE" of Fig. 2, to prevent the compressor from being forced into the "SURGE REGION" prior to opening of the valve body 36 to relieve the flow of pressurized gas from the compressor to prevent surge. As a result of the time ΔT in Fig. 4A required for the ΔP sensor 24 to sense the surge condition in the outlet 22, the operation point of the compressor on the "CONSTANT SPEED LINE" of Fig. 2 must be displaced sufficiently far from the "SURGE LINE" to allow the valve 36 to be opened so that the operation of the compressor becomes inefficient relative to that that could be obtained if a more rapidly operating ΔP switch were available. Rapid transients of the airflow decreasing from the duct 22 will always result in compressor surge as in 4A.
United States Patents 4,300,587, 4,781,524 and 4,810,163 disclose compressor controls. Patent 4,810,163 discloses a system to prevent unstable turbo- compressor behavior in which the feed medium flows in surges or periodically from the compressor or discharge side back to the suction side. An overboard valve 9 is used to relieve the aforementioned condition. Patent 4,300,587 discloses a relief valve for limiting discharge pressure of an aircraft cabin pressurization system. United States Patent 4,781,524 discloses a system for detecting pressure surges in a turbo compressor. Disclosure of Invention
The present invention provides a simple high speed surge protection system and a differential pressure sensor with improved detection response. With the invention, the opening of an overboard valve to relieve pressure at the discharge of a compressor to prevent surge is controlled by a pressure transducer having first and second gas lines respectively coupled to the throat of a restriction and an upstream side of the restriction with the first gas line having a pressure propagation time shorter than a pressure propagation time of the second gas line to increase the speed of response of opening of the overboard valve. As used herein, the terminology, "pressure propagation time" means the time for a pressure perturbation to flow from a sensing point in a fluid line to an input of the pressure transducer. The pressure propagation times of the first and second gas lines are a function of diameter of the first and second lines, a function of the length of the first and second lines and a volume of the pressure transducer. Furthermore, if a restriction is disposed in the line coupled between the upstream side of the restriction and an inlet to the pressure transducer, pressure propagation time is further a function of the degree of restriction of the second line from its inner diameter by the restriction.
A compressor with surge control in accordance with the invention includes a rotor for receiving gas at an inlet and providing pressurized gas at an outlet; an outlet line coupled to the outlet for outputting pressurized gas; a flow measuring device (typically a venturi) disposed in the outlet gas line for restricting the flow of gas in a line which causes a pressure drop in the outlet line; a bypass valve disposed in the outlet line upstream of an inlet of the flow measuring device which has an open state and a closed state controlled by a control signal with the valve in the open state permitting pressurized gas from the compressor to be discharged from the outlet line prior to flow to the flow meaning device; and a pressure sensor having a first gas line coupled to the flow measuring device and a second gas line coupled to the outlet line upstream of the flow measuring device with the first gas line having a pressure propagation time shorter than a pressure propagation time of the second gas line, the pressure sensor producing the control signal in response to a drop in pressure drop across the pressure sensor dropping below a predetermined threshold which cause the bypass valve to open. The pressure sensor can be a single ΔP valve. The flow sensor can be by means of a venturi. The compressor may be operated with a constant rotor speed outside of a surge region defined by a relationship of pressure drop across the inlet and outlet versus pressure drop across the flow measuring device; and a difference in pressure propagation times of the first and second conduits causes opening of the bypass valve in response to a pressure rise downstream from an outlet of the flow measuring device prior to the pressure rise causing operation of the compressor to move into the surge region.
A pressure sensor for sensing a drop in magnitude of pressure across two points in a fluid stream in accordance with the invention includes a first line coupled to a first point in the fluid stream having a lower pressure when fluid is flowing in the fluid stream and to a pressure transducer; a second line coupled to a second point in the fluid stream having a higher pressure when fluid is flowing in the second stream and to the pressure transducer; and wherein the first line has a pressure propagation time shorter than a pressure propagation time of the second line with the pressure transducer producing an output signal when the magnitude of the pressure drop between the two points is less than a threshold. The pressure propagation times are a function of diameter of the first and second lines, a function of the length of the first and second lines, and a volume of the pressure transducer. Furthermore, a restriction may be disposed in the second line and the pressure propagation times are a function of the restriction of the second line by the restriction.
Brief Description of Drawings
Fig. 1 illustrates a prior art compressor using a ΔP operated valve for surge protection.
Fig. 2 illustrates the operational characteristic of a prior art compressor such as that illustrated in Fig. 1.
Fig. 3 illustrates an embodiment of the present invention. Figs. 4A and 4B respectively illustrate the response characteristics of the prior art system of Fig. 1 and the embodiment of Fig. 3.
Best Mode for Carrying Out the Invention Fig. 3 illustrates an embodiment 100 of the present invention. Like reference numerals identify the same parts in Figs. 1 and 3. The embodiment 100 of Fig. 3 differs from the prior art of Fig. 1 in that the first gas line 27 coupled to the flow measuring device 16 which may be a venturi and to one side of a diaphragm 29 of the ΔP sensor 24, which functions as a differential pressure transducer, has a pressure propagation time shorter than a pressure propagation time of the second fluid line 31 coupled to the upstream side 18 of the venturi 16 and to the other side of the diaphragm of the ΔP valve. A pressure perturbation requires a time interval to travel completely through the fluid lines 27 and 31 which is proportional to the pressure propagation time. Therefore, the design of the first and second fluid lines to have shorter and longer pressure propagation times determines the time interval that pressure perturbations are coupled to the sides of the diaphragm 29 which are caused by a restriction of the outlet 22. As a consequence of the first fluid line 27 being designed to have pressure propagation time shorter than the pressure propagation time of the second fluid line 31, a response of the ΔP sensor 24 to a pressure increase in the output 22 of the outlet 14 which causes a surge condition is more quickly detected than that of prior art as illustrated in Fig. 4A. With reference to Fig. 4B which illustrates the time response of the embodiment 100 of the present invention to a rise in pressure in the outlet 22, it is seen that time length ΔT required for the relative pressures PQ and Pv to become equal is shorter than the time length ΔT as in the prior art of Fig. 4A when the first fluid line 27 has a shorter pressure propagation time than the second fluid line 31. The response of the ΔP sensor 24 producing an output signal applied to the servo mechanism 34 in response to a pressure rise in the outlet 22 which could result in a surge condition is enhanced. With reference to the operating characteristic of the prior art of Fig. 2, the present invention permits the "TYPICAL OPERATING POINT" to be positioned closer to the "SURGE LINE" as a consequence of the decreased time interval ΔT required for the ΔP sensor 24 to sense the equalization of pressures P0 and Pv. As a result, the compressor may be operated at a higher efficiency condition than with the prior art while avoiding the "SURGE REGION" of operation.
Several factors influence the pressure propagation time of the fluid lines 27 and 31. Pressure propagation times are a function of the diameter of the first and second lines 27 and 31. The pressure propagation time increases as a function of increasing diameter. Additionally, the pressure propagation time of the first and second lines 27 and 31 are a function of the length of the first and second fluid lines. The pressure propagation time increases with increasing length. The pressure propagation times of the first and second fluid lines 27 and 31 are a function of the volume of the pressure sensor in which the diaphragm 29 is disposed for detecting differential pressure between the first and second fluid lines. The pressure propagation time increases as the volume of the chamber containing the diaphragm 29 increases. Finally, the 5 pressure propagation time of the second fluid line 31 may be increased relative to the first fluid line 27 by providing a restriction 102 within the second line. The pressure propagation time increases as the amount of restriction increases in the second line from its
10 nominal inner diameter. In order to produce the most rapid response characteristic for the ΔP valve 24, the first fluid line 27 should be designed to have the shortest possible pressure propagation time and the second fluid line 31 should be designed to have a
15 longer propagation time such that there is a crossover in the relative pressures P0 and Pv as indicated in Fig. 4B as quickly as possible after the pressure perturbation in the outlet 22 indicative of a surge condition occurs.
20 While the invention has been described in terms of its preferred embodiment, it should be understood that numerous modifications may be made thereto without departing from the spirit and scope of the invention as defined in the appended claims. For example, while the
25 pressure sensor of the present invention is used for sensing pressure perturbations in gas lines, this pressure sensor could be in the form of a pressure switch which produces an electrical signal to an electrically (solenoid) operated version of the
30 valve 36. The restriction used for measuring the compressor outlet flow by means of the pressure drop (ΔP) can be a venturi, or the flow measurement could be in the form of a total pressure sensor and a static pressure sensor both in the outlet gas stream with ΔP being derived from the Total Pressure - Static Pressure. It is intended that all such modifications fall within the scope of the appended claims.

Claims

Claims
1. A compressor with surge control comprising: a rotor receiving gas at an inlet and providing pressurized gas at an outlet; an outlet line coupled to the outlet for providing pressurized gas; a flow measuring device disposed in the outlet line for sensing the flow of gas in the line which causes a pressure drop in the outlet line; a bypass valve disposed in the outlet line upstream of an inlet of the flow measuring device which has an open state and a closed state controlled by a control signal with the valve in the open state permitting pressurized gas discharged from the compressor to be discharged from the outlet line prior to flow to the flow measuring device; and a pressure sensor having a first gas line coupled to the flow measuring device and a second gas line coupled to the outlet line upstream of the flow measuring device with the first gas line having a pressure propagation time shorter than a pressure propagation time of the second gas line, the pressure sensor producing the control signal in response to a drop in pressure across the pressure sensor below a threshold which causes the bypass valve to open.
2. A compressor in accordance with claim 1 wherein: the pressure sensor is a ΔP valve.
3. A compressor in accordance with claim 1 wherein: the flow measuring device is a venturi.
4. A compressor in accordance with claim 2 wherein: the flow measuring device is a venturi.
5. A compressor in accordance with claim 1 wherein: the compressor is operated with a constant rotor speed outside of a surge region defined by a relationship of pressure drop across the inlet and outlet versus pressure drop across the flow measuring device; and a relative pressure propagation time of the first and second gas lines causes opening of the bypass valve in response to a pressure rise downstream from an outlet of the flow measuring device prior to the pressure rise causing operation to move into the surge region.
6. A compressor in accordance with claim 2 wherein: the compressor is operated with a constant rotor speed outside of a surge region defined by a relationship of pressure drop across the inlet and outlet versus pressure drop across the flow measuring device; and a relative pressure propagation time of the first and second gas lines causes opening of the bypass valve in response to a pressure rise downstream from an outlet of the flow measuring device prior to the pressure rise causing operation to move into the surge region.
7. A compressor in accordance with claim 3 wherein: the compressor is operated with a constant rotor speed outside of a surge region defined by a relationship of pressure drop across the inlet and outlet versus pressure drop across the flow measuring device; and a relative pressure propagation time of the first and second gas lines causes opening of the bypass valve in response to a pressure rise downstream from an outlet of the flow measuring device prior to the pressure rise causing operation to move into the surge region.
8. A compressor in accordance with claim 4 wherein: the compressor is operated with a constant rotor speed outside of a surge region defined by a relationship of pressure drop across the inlet and outlet versus pressure drop across the flow measuring device; and a relative pressure propagation time of the first and second gas lines causes opening of the bypass valve in response to a pressure rise downstream from an outlet of the flow measuring device prior to the pressure rise causing operation to move into the surge region.
9. A compressor in accordance with claim 1 wherein: the pressure propagation times are a function of diameter of the first and second gas lines, a function of the length of the first and second gas lines, and of a volume of the pressure sensor.
10. A compressor in accordance with claim 2 wherein: the pressure propagation times are a function of diameter of the first and second gas lines, a function of the length of the first and second gas lines, and of a volume of the pressure sensor.
11. A compressor in accordance with claim 3 wherein: the pressure propagation times are a function of diameter of the first and second gas lines, a function of the length of the first and second gas lines, and of a volume of the pressure sensor.
12. A compressor in accordance with claim 4 wherein: the pressure propagation times are a function of diameter of the first and second gas lines, a function of the length of the first and second gas lines, and of a volume of the pressure sensor.
13. A compressor in accordance with claim 5 wherein: the pressure propagation times are a function of diameter of the first and second gas lines, a function of the length of the first and second gas lines, and of a volume of the pressure sensor.
14. A compressor in accordance with claim 6 wherein: the pressure propagation times are a function of diameter of the first and second gas lines, a function of the length of the first and second gas lines, and of a volume of the pressure sensor.
15. A compressor in accordance with claim 7 wherein: the pressure propagation times are a function of diameter of the first and second gas lines, a function of the length of the first and second gas lines, and of a volume of the pressure sensor.
16. A compressor in accordance with claim 8 wherein: the pressure propagation times are a function of diameter of the first and second gas lines, a function of the length of the first and second gas lines, and of a volume of the pressure sensor.
17. A compressor in accordance with claim 9 wherein: a restriction is disposed in the second line; and the pressure propagation times are a function of the restriction of the second gas line by the restriction.
18. A compressor in accordance with claim 10 wherein: a restriction is disposed in the second line; and the pressure propagation times are a function of the restriction of the second line by the restriction.
19. A compressor in accordance with claim 11 wherein: a restriction is disposed in the second line; and the pressure propagation times are a function of the restriction of the second line by the restriction.
20. A compressor in accordance with claim 12 wherein: a restriction is disposed in the second line; and the pressure propagation times are a function of the restriction of the second line by the restriction.
21. A compressor in accordance with claim 13 wherein: a restriction is disposed in the second line; and the pressure propagation times are a function of the restriction of the second line by the restriction.
22. A compressor in accordance with claim 14 wherein: a restriction is disposed in the second line; and the pressure propagation times are a function of the restriction of the second line by the restriction.
23. A compressor in accordance with claim 15 wherein: a restriction is disposed in the second line; and the pressure propagation times are a function of the restriction of the second line by the restriction.
24. A compressor in accordance with claim 16 wherein: a restriction is disposed in the second line; and the pressure propagation times are a function of the restriction of the second line by the restriction.
25. A pressure sensor for sensing a drop in magnitude of pressure between two points in a fluid stream comprising: a first line coupled to a first point in the fluid stream having a lower pressure when fluid is flowing in the fluid stream and to a pressure transducer; a second line coupled to a second point in the fluid stream having a higher pressure when fluid is flowing in the fluid stream and to the pressure transducer; and wherein the first line has a pressure propagation time shorter than a pressure propagation time of the second line with the pressure transducer producing an output signal when the magnitude of pressure drop between the two points is less than a threshold.
26. A pressure sensor in accordance with claim 25 wherein: the pressure propagation times are a function of diameter of the first and second lines, a function of the length of the first and second lines, and a volume of the pressure transducer.
27. A pressure sensor in accordance with claim 26 wherein: a restriction is disposed in the second line; and the pressure propagation times are a function of the restriction of the second line by the restriction.
28. A pressure sensor in accordance with claim 25 wherein: the fluid is a gas.
29. A pressure sensor in accordance with claim 25 wherein: the fluid is a liquid.
PCT/US1990/006217 1989-11-21 1990-10-26 Simple surge control for compressors with improved response WO1991007712A1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US43968689A 1989-11-21 1989-11-21
US439,686 1989-11-21

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Cited By (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2680394A1 (en) * 1991-08-16 1993-02-19 Normalair Garrett Ltd ANTI-PUMPING SYSTEM AND APPARATUS FOR AN AIR COMPRESSOR.
EP0622287A1 (en) * 1993-04-30 1994-11-02 KRAPF & LEX NACHF. VERKEHRSTECHNIK GmbH & Co.KG Device for pressure limitation in high speed railway vehicles
US5507108A (en) * 1993-02-08 1996-04-16 U.S. Philips Corporation Steam iron with scale prevention
WO1998015456A1 (en) * 1996-10-07 1998-04-16 Trilectron Industries, Inc. Demand system for pneumatic source
EP1258792A1 (en) * 2001-05-16 2002-11-20 Esec Trading S.A. Pressure regulator
WO2003067355A2 (en) * 2002-02-01 2003-08-14 Perseptive Biosystems, Inc Programmable tracking pressure regulator for control of higher pressures in microfluidic circuits
US6681797B2 (en) 2001-05-16 2004-01-27 Esec Trading Sa Pressure transducer
EP3486631A1 (en) * 2017-11-17 2019-05-22 Hamilton Sundstrand Corporation Electronic control system tester

Citations (5)

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Publication number Priority date Publication date Assignee Title
US2406181A (en) * 1943-01-14 1946-08-20 Wright Aeronautical Corp Flowmeter
GB1080013A (en) * 1963-05-10 1967-08-23 Dehavilland Aircraft Improvements in or relating to mass flow measuring apparatus
US4300587A (en) * 1979-11-30 1981-11-17 The Garrett Corporation Relief valve
US4768605A (en) * 1987-09-04 1988-09-06 Trw Inc. Apparatus for use in a power steering system
US4781524A (en) * 1987-02-12 1988-11-01 Man Gutehoffnungshuette Gmbh Method and apparatus for detecting pressure surges in a turbo-compressor

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2406181A (en) * 1943-01-14 1946-08-20 Wright Aeronautical Corp Flowmeter
GB1080013A (en) * 1963-05-10 1967-08-23 Dehavilland Aircraft Improvements in or relating to mass flow measuring apparatus
US4300587A (en) * 1979-11-30 1981-11-17 The Garrett Corporation Relief valve
US4781524A (en) * 1987-02-12 1988-11-01 Man Gutehoffnungshuette Gmbh Method and apparatus for detecting pressure surges in a turbo-compressor
US4768605A (en) * 1987-09-04 1988-09-06 Trw Inc. Apparatus for use in a power steering system

Cited By (12)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2680394A1 (en) * 1991-08-16 1993-02-19 Normalair Garrett Ltd ANTI-PUMPING SYSTEM AND APPARATUS FOR AN AIR COMPRESSOR.
US5507108A (en) * 1993-02-08 1996-04-16 U.S. Philips Corporation Steam iron with scale prevention
EP0622287A1 (en) * 1993-04-30 1994-11-02 KRAPF & LEX NACHF. VERKEHRSTECHNIK GmbH & Co.KG Device for pressure limitation in high speed railway vehicles
WO1998015456A1 (en) * 1996-10-07 1998-04-16 Trilectron Industries, Inc. Demand system for pneumatic source
US5993163A (en) * 1996-10-07 1999-11-30 Trilectron Industries, Inc. Demand system for pneumatic source with controller responsive to bypass air flow rate
EP1258792A1 (en) * 2001-05-16 2002-11-20 Esec Trading S.A. Pressure regulator
US6681797B2 (en) 2001-05-16 2004-01-27 Esec Trading Sa Pressure transducer
WO2003067355A2 (en) * 2002-02-01 2003-08-14 Perseptive Biosystems, Inc Programmable tracking pressure regulator for control of higher pressures in microfluidic circuits
US6662818B2 (en) 2002-02-01 2003-12-16 Perseptive Biosystems, Inc. Programmable tracking pressure regulator for control of higher pressures in microfluidic circuits
WO2003067355A3 (en) * 2002-02-01 2004-03-04 Perseptive Biosystems Inc Programmable tracking pressure regulator for control of higher pressures in microfluidic circuits
EP3486631A1 (en) * 2017-11-17 2019-05-22 Hamilton Sundstrand Corporation Electronic control system tester
US10620091B2 (en) 2017-11-17 2020-04-14 Hamilton Sundstrand Corporation Electronic control system tester

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